The present invention relates to a thermosensitive recording material, in particular, to a thermosensitive recording material with photo-fixing ability. More precisely, the present invention relates to a diazo-type thermosensitive recording material which colors in response to recording by thermal heads at a certain temperature; which loses coloring ability in the non-recorded areas upon photo-irradiation; and which cannot thereafter be further colored even if heated again.
Thermosensitive recording materials are being used not only for copying material from books and documents, but also as output recording sheets for computers, facsimile apparatus and medical analytical instruments, as well as for thermosensitive-recording-type magnetic tickets and thermosensitive-recording-type labels. Because of the ease of automatic recording, thermosensitive recording materials can also be utilized for securities, merchandise coupons, entrance tickets, certificates, payment slips and the like. However, thermosensitive recording materials for such uses must be image-fixable in order to maintain the integrity of the recorded information.
Conventionally, as an image-fixable thermosensitive recording material, a diazo-type thermosensitive recording material is known, which utilizes the coloring reaction between a diazonium compound and a coupler. However, the conventional diazo-type thermosensitive recording material cannot be used in practice because of its slow thermal response to a thermal head and poor preservability. Especially in the field of facsimiles, a thermosensitive-recording material with rapid recording (rapid coloring) is required in order to minimize communication costs. This conventional diazo-type material does not satisfactorily meet such a requirement. Therefore, it is necessary to improve the diazo photosensitive paper so as to cause the coloring reaction to occur efficiently by minimum energy consumption.
In another conventional diazo photosensitive paper, the coloring reaction can be caused to occur so as to provide sufficiently high image density by use of ammonium water or an alkaline solution as a developer, or by sufficient heat application, so long as it is used in a conventional manner with a conventional slow development speed.
Under such circumstances, there have been proposed improved thermosensitive recording materials, which utilize the coloring reaction between a diazonium compound and a coupler.
For instance, in a reference entitled "Light Sensitive System" by J. Kosar (published by John and Wiley and Sons in 1965), there is proposed a thermosensitive recording material utilizing a basic material in its coloring system, for instance, inorganic ammonium salts, organic ammonium salts, and organic amines such as urea, thiourea, guanidine and biuret, in order to place the coloring system in an alkaline atmosphere for accelerating the thermal development.
In Japanese Patent Publication No. 57-19407, there are disclosed thermal reactive diazo-type recording sheets in which as a basic material for neutralizing an acid, imidazole or imidazoline derivatives are employed. These additives, however, have the shortcomings of decreasing the development performance after a prolonged storage of the recording materials, due to the sublimation properties thereof. Except for the recording material utilizing imidazole, the above-mentioned recording materials do not yield sufficiently high image density, and yet again, those conventional diazo-type materials do not satisfactorily meet the requirements for use with a thermal head or pen.
Further, in Japanese Patent Publication No. 53-27604, there is disclosed a diazo-type thermosensitive recording sheet in which benzimidazole derivatives, which are less basic than imidazole, are employed. This diazo-type thermosensitive recording sheet does not yield sufficiently high image density, either.